Problem: $\dfrac{9}{12} + \dfrac{7}{4} = {?}$
$ = {\dfrac{9 \times 1}{12 \times 1}} + {\dfrac{7 \times 3}{4 \times 3}} $ $ = {\dfrac{9}{12}} + {\dfrac{21}{12}} $ $ = \dfrac{{9} + {21}}{12} $ $ = \dfrac{30}{12}$